The Conjugate Addition of Novel Nucleophiles and Catalytic Intramolecular Tandem [1,5]-Hydride Shift / Cyclization and Friedel-Crafts Acylation with Alkylidene Meldrum’s Acid Derivatives

Abstract

Investigations into the conjugate addition of phenols and sp3-hybridized carbons bound to tin, boron and silicon by transition metal catalysts through novel transmetallation pathways were undertaken with limited success. An intramolecular Lewis acid-catalyzed tandem [1,5]-hydride shift / cyclization and Friedel-Crafts acylation reaction with alkylidene Meldrum’s acid derivatives has been accomplished.

The use of metal phenolates as nucleophiles for transition metal catalyzed conjugate addition onto alkylidene Meldrum’s acids is explored, and the ambident nucleophilic property of metal phenolates allow for the C-alkylation and O-acylation with alkylidene Meldrum’s acids, producing substituted 3,4-dihydrocoumarins in modest yields.

The transmetallation of rhodium complexes with alkyl boron, tin and silicon derivatives and subsequent conjugate addition onto alkylidene Meldrum’s acid derivatives is investigated without success.

An intramolecular Lewis acid-catalyzed [1,5]-hydride shift / cyclization reaction promoted by electron-rich aromatic rings is employed with alkylidene Meldrum’s acid derivatives to furnish spiro Meldrum’s acids in excellent yields. These can subsequently be used as electrophiles in the Friedel-Crafts acylation reaction, and a tandem, one-pot variation of this reaction has been accomplished in moderate to good yields. Preliminary investigations into the scope and limitations of this transformation are outlined.